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Inexpensive IC based phono preamp for LOMC
http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=4441
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Author:  mwhouston [ 11 Feb 2014, 07:19 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

You need to turn about 0.005V into 1V. That requires gain.

Author:  mwhouston [ 12 Feb 2014, 08:25 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

I was informed by my audio buddy, Dave, that the Japanese like to lacquer things. If it is not timber on some box or art pieces it is audio components. They just want to go around lacquering things. Anything, it doesn't matter. If you are Japanese and can shed some light on this please do. Lacquer some information on us.

So this got my thinking. I have some spray cans of some fine lacquers (yes I know Samurais didn't have spray cans but that's not my fault). I also can lacquer. Tomorrow I will bare the inners of my Mimic preamp and lacquer it in the time honored Japanese method - "Method de Lacquer". Doesn't sound Japanese to me??? More like French. Regardless; Shintaro, step aside.

Author:  gofar99 [ 12 Feb 2014, 09:12 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Say what? Spray everything in place? Reminds me of a very old radio I was going to restore. That is until I opened it up. They apparently assembled everything in a floating sort of spider web and then poured Bakelite over it. Just the termination wires came out of the brick. Impossible to service.

Good listening
Bruce

Author:  mwhouston [ 12 Feb 2014, 17:36 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

gofar99 wrote:
Say what? Spray everything in place? Reminds me of a very old radio I was going to restore. That is until I opened it up. They apparently assembled everything in a floating sort of spider web and then poured Bakelite over it. Just the termination wires came out of the brick. Impossible to service.

Yes I thought I may mask-off all bar the cct. Brd. then use a heavy polyurethane spray. What have I got to lose?

Hey I have got into Pandora since my Oppo has the app built in after the last firmware upgrade.

Author:  mwhouston [ 05 Mar 2014, 07:35 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

I chickened-out lacquering my preamp but I did add more bitumanised Al. More underneath the enclosure, on the chip, switch and cct. brd. Can't hear a difference but it has to be better. Doesn't it??
Attachment:
BAl.jpg

Author:  gofar99 [ 05 Mar 2014, 08:59 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Hi Mark, It is amazing how well something simple like this can work. It does require a good OP amp though. The OPA2134 is perfect for it. I was listening to it on my Sota/Origin Live/AT-33PTG-II yesterday and it is hard to fault. Not as refined as the Groove and a bit less warm, but easy to listen too and very quiet. I add the NAB eq to all mine (two external and one built into a integrated preamp) and mostly use them that way. Far better and quieter than the playback preamps in the recorder.

Along the same lines I put together an IC based SUT replacement pre-preamp. I set the gain at 10(it could be any value up to 100 or more). With another OPA2134 doing the amp chores and battery power by 2 nine volt cells. I added a LED power on indicator as well. I'll have to get with my partner on the LEDs as they go with some of our kits. Immensely efficient. At 0.1ma it is quite bright. You would not think a green LED with a 100K resistor on 9 volts would even be visible. Not these ones. Quite easy to see. Back to the prepre. Off scale on residual noise. I can't measure reliably below -100 db. Response is flat from 10HZ to 600,000HZ. The top -1db point is nearly at 1 meg. Overkill for sure. However in the listening area the Lundhalls still sound better to me. It isn't flawed in any obvious way, more likely the Lundhalls are, but I like the way the sound better. A good instrumentation amp though for use in front of a scope or meter at any rate. The input can range from zilch microvolts to about 0.5 volts and still be linear. I'll post a schematic when I get a chance.

Good listening
Bruce

Author:  mwhouston [ 05 Mar 2014, 14:15 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

As you can see from my latest post I'm still using mine. Got some tube kits but they are a way off. Enjoying the Silver Dragon, VoXDeuX65 combo with the stereo subbies, VoXItBassO at the moment. One box set of 3 LPs I'm enjoying is a 1965 recording of Handle's Messiah. I can't stop playing the bloody thing and it goes for 2.5 hours. Of course Mimic is doing the grove to audio decoding.

Author:  Mightym [ 10 Mar 2014, 22:02 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Bruce, if you decide to offer a kit for these, and the kit is ready by Lone Star Audio Fest....

I'd like to have one, and will gladly pick it up there, or what ever needs to be done.

I'm still enough of a newb that building a kit appeals to me over trying to flesh one of these out on my own.

I always have difficulty with the grounding issues...

looking forward to the show too.

John

Author:  gofar99 [ 15 Mar 2014, 14:23 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Hi, Sorry for the delay in responding I have been sick for over a week (pneumonia). The preamp is a virtual certainty as a kit, but it takes us a while to get stuff to the market. As a smallish US company that tries hard to source everything here we are forced to go on the slower side. On a wild guess (as it is now number 2 in the development pipe) I would guess about September for a release date. Presently a guitar head amp is in front of it. There are three more behind it as well.

You can hear them at LSAF as I will have two there. One will be on a reel to reel tape recorder and one for phono use. All are configurable in NAB, MM/MI and LOMC modes. I plan on using the one with modified Pro-ject turntable with an Origin Live tone arm and an AT-F7 LOMC (and some other cartridges like an OM30, Denon DL110 and I might be temped to bring my AT33-PTG/II. It is a killer, but much more delicate and above the price range I would expect to be used the the preamp). The planned initial combination is somewhat above the entry level, but not nearly at the other extreme. Something about like most folks would want to use. It brings up the ancient questions on how much is the right amount to spend on the turntable end of things. There is no great answer. But considering that vinyl tends to be costly (for new and high demand vintage LPs) and the LPs can be damaged with poor equipment the price of the TT gear should be equated with the performance level you seek. Fortunately there are now some really good players in the under $300US range. Ones by Orbit are well thought of but really minimal in features and surprisingly the Music Hall USB-1 was well regarded by Stereophile. My personal thoughts go to the entry level Pro-jects but vintage gear can be obtained in good condition that will out perform they new ones in the same price range. BTW I will also be using a Groove all tube phono preamp with Lundhall input transformers as a comparison.

Good listening
Bruce

Author:  mwhouston [ 15 Mar 2014, 19:25 ]
Post subject:  Re: Inexpensive IC based phono preamp for LOMC

Slightly off thread: a Melbourne Audio Club member asked me to do some fine soldering for him. He had broken a wire on the inside of his AT cartridge. It appears there are some who "denude" their cartridges in an effort to reduce resonance, weight, etc. The practice involves removing motor covers and guards to bare the motor to the world. In this case two extremely fine wires, which extended from the motor to the posts at the back of the cartridge, were broken.

I had several attempts to get a good view of the damage but in the end deemed it to hard. You would probably need a low power microscope to do the work. Fortunately it is not a expensive cartridge and the owner has a few better ones. The owner is a vinyl only audiophile who very rarely plays CDs. For me I wouldn't go near this practice. My Ortofon is a $1000 cart and there is no way I would try and lever bits off it. No Sir!

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